It's already been established that there are limits to Free Speech. One is free to scream "Fire!" in their private residence until they are blue in the face. One is certainly not free to do the same in a crowded public place.
One is free to walk around spewing their personal opinion all day long. One is not free to walk around following somebody and spewing that same opinion at them over and over.
The lawyer in this case is basically trying to justify his client's actions by calling them anonymous free speech, a right protected by the Constitution. Unfortunately, his client's action are more akin to posting fliers with ads on other peoples' private property, using stolen supplies and driving a stolen vehicle.